The Children's Cancer Center at St. Louis Children's Hospital is the only such center within a 200-mile radius and offers multimodal therapy to children with malignant disease. At the time of diagnosis of a malignant disease in a child, the clinical findings are reviewed and management is discussed at the Pediatric Tumor Conference by attending pediatric oncologists, radiation therapists, surgeons and pathologists in order to assure that each child receives optimal therapy. In collaboration with the Southwest Oncology Group the Center offers access to new intensive therapeutic regimens and experimental compounds to approximately 200 children with malignant disease. Extensive ancillary studies, both at the clinical and preclinical level, are underway in parallel with the oncology studies in children. Thus, the bone marrow stem cell culture technique is being used to evaluate the effects of chemotherapeutic agents on granulocytopoiesis. The spleen colony assay technique is being used to quantitate the effects of different doses and schedules of combination chemotherapy and chemotherapy plus radiation therapy on malignant cells and normal hematopoietic stem cells. Parallel in vitro studies are being done. Results from these preclinical studies are presently being applied to scheduling of combination chemotherapy regimens in children. Hopefully a more rational basis for therapy and thus more effective therapy will evolve.